.\" Process this file with
.\" groff -man -Tascii patchelf.1
.\"
.TH PATCHELF 1 "JULY 2022" PATCHELF "User Manuals"
.SH NAME
patchelf - Modify ELF files

.SH SYNOPSIS
.B patchelf
.I OPTION
.B
.I FILE
.SM ...
.B

.SH DESCRIPTION

PatchELF is a simple utility for modifying existing ELF executables
and libraries.  It can change the dynamic loader ("ELF interpreter")
of executables and change the RPATH of executables and libraries.

.SH OPTIONS

The single option given operates on each FILE, editing in place.

Any option taking a string argument can also take a file by prefixing the
argument with the @ symbol. See EXAMPLES

.IP "--page-size SIZE"
Uses the given page size instead of the default.

.IP "--set-interpreter INTERPRETER"
Change the dynamic loader ("ELF interpreter") of executable given to
INTERPRETER.

.IP --print-interpreter
Prints the ELF interpreter of the executable.

.IP --print-os-abi
Prints the OS ABI of the executable (EI_OSABI field of an ELF file).

.IP "--set-os-abi ABI"
Changes the OS ABI of the executable (EI_OSABI field of an ELF file).
The ABI parameter is pretty flexible. For example, you can specify it
as a "Linux", "linux", or even "lInUx" - all those names will set EI_OSABI
field of the ELF header to the value "3", which corresponds to Linux OS ABI.
The same applies to other ABI names - System V, FreeBSD, Solaris, etc.

.IP --print-soname
Prints DT_SONAME entry of .dynamic section.
Raises an error if DT_SONAME doesn't exist.

.IP "--set-soname SONAME"
Sets DT_SONAME entry of a library to SONAME.

.IP "--set-rpath RUNPATH"
Change the DT_RUNPATH of the executable or library to RUNPATH.

.IP "--add-rpath RUNPATH"
Add RUNPATH to the existing DT_RUNPATH of the executable or library.

.IP --remove-rpath
Removes the DT_RPATH or DT_RUNPATH entry of the executable or library.

.IP --shrink-rpath
Remove from the DT_RUNPATH or DT_RPATH all directories that do not contain a
library referenced by DT_NEEDED fields of the executable or library.

For instance, if an executable references one library libfoo.so, has
an RPATH "/lib:/usr/lib:/foo/lib", and libfoo.so can only be found
in /foo/lib, then the new RPATH will be "/foo/lib".

.IP "--allowed-rpath-prefixes PREFIXES"
Combined with the "--shrink-rpath" option, this can be used for
further rpath tuning. For instance, if an executable has an RPATH
"/tmp/build-foo/.libs:/foo/lib", it is probably desirable to keep
the "/foo/lib" reference instead of the "/tmp" entry.

.IP --print-rpath
Prints the DT_RUNPATH or DT_RPATH for an executable or library.

.IP --force-rpath
Forces the use of the obsolete DT_RPATH in the file instead of
DT_RUNPATH. By default DT_RPATH is converted to DT_RUNPATH.

.IP "--add-needed LIBRARY"
Adds a declared dependency on a dynamic library (DT_NEEDED).
This option can be given multiple times.

.IP "--replace-needed LIB_ORIG LIB_NEW"
Replaces a declared dependency on a dynamic library with another one (DT_NEEDED).
This option can be given multiple times.

.IP "--remove-needed LIBRARY"
Removes a declared dependency on LIBRARY (DT_NEEDED entry). This
option can be given multiple times.

.IP --print-needed
Prints all DT_NEEDED entries of the executable.

.IP "--no-default-lib"
Marks the object so that the search for dependencies of this object will ignore any
default library search paths.

.IP "--no-sort"
Do not sort program headers or section headers.  This is useful when
debugging patchelf, because it makes it easier to read diffs of the
output of "readelf -a".

.IP "--add-debug-tag"
Adds DT_DEBUG tag to the .dynamic section if not yet present in an ELF
object. A shared library (-shared) by default does not receive DT_DEBUG tag.
This means that when a shared library has an entry point (so that it
can be run as an executable), the debugger does not connect to it correctly and
symbols are not resolved.

.IP "--print-execstack"
Prints the state of the executable flag of the GNU_STACK program header, if present.

.IP "--clear-execstack"
Clears the executable flag of the GNU_STACK program header, or adds a new header.

.IP "--set-execstack"
Sets the executable flag of the GNU_STACK program header, or adds a new header.

.IP "--rename-dynamic-symbols NAME_MAP_FILE"
Renames dynamic symbols. The name map file should contain lines
with the old and the new name separated by spaces like this:

old_name new_name

Symbol names do not contain version specifier that are also shown in the output of the nm -D command from binutils. So instead of the name write@GLIBC_2.2.5 it is just write.

.IP "--no-clobber-old-sections"
Do not clobber old section values.

patchelf defaults to overwriting replaced header sections with garbage to ensure they are not
used accidentally. This option allows to opt out of that behavior, so that binaries that attempt
to read their own headers from a fixed offset (e.g. Firefox) continue working.

Use sparingly and with caution.

.IP "--output FILE"
Set the output file name.  If not specified, the input will be modified in place.

.IP --debug
Prints details of the changes made to the input file.

.IP --version
Shows the version of patchelf.

.SH EXAMPLES

To use the contents on an external file as a parameter:

.RS
$ patchelf a.out --add-rpath @/tmp/generated-rpath.bin
.RE

To change the RPATH of a binary. Note that
.BR $ORIGIN
is a special symbol used by the loader, so must be quoted.

.RS
patchelf --set-rpath '$ORIGIN/../lib64' a.out
.RE


.SH AUTHOR
Eelco Dolstra <e.dolstra@tudelft.nl>

.SH "SEE ALSO"
.BR elf (5),
.BR ld.so (8)


